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modular and scalable devices with advanced feature stacks. To help storage managers get up to speed, we provide a snapshot of newer NAS features and a sampling of some vendors who sell NAS products.

Clustered or scale-out network attached storage (NAS) products

Nowadays, network attached storage products often offer increased scalability and performance compared to the standalone boxes of yesteryear. NAS' ability to scale its capacity means it's increasingly being used in clusters that mirror the growth in compute clusters.

So-called clustered or scale-out NAS dispenses with the idea of storage controllers or NAS filer heads. The architecture comprises hardware nodes that contain disk, cache and CPU resources with a node being a peer in a cluster.

Among the benefits of scale-out NAS are single name space, which allows users and applications to access and search data scattered across geographical locations and clustered storage devices without needing to know their location; data protection features, such as data backup and replication; flexibility, to grow or shrink capacity by adding or removing devices; ease of management; and the ability to use a single storage management system across multiple devices.

Scale-out/clustered NAS is well-suited to high-volume, small file size content serving, such as delivering online services to consumers.

Data deduplication

Data deduplication technology is often incorporated into NAS devices. Data deduplication means the storage system retains only one of multiple copies of a piece of data, removing later iterations while inserting a pointer to the original.

It is commonly used for compressing backups before the data is sent to the virtual tape library (VTL). For example, backing up a department full of Windows PCs would otherwise mean moving and storing dozens of gigabytes of identical OS and program data per machine.

Flash drives

Seen primarily in the form of USB-attached memory, flash memory can be found in some enterprise NAS products. Its lack of moving parts mean it consumes less space and energy and, in the right configuration, it is faster. Vendors such as Sun Microsystems and EMC have added flash-based storage into some of their products to insert a tier zero above the existing tiers in a tiered architecture for highly transactional access that can take the best advantage of its speed.

Multiprotocol access

Traditionally, direct-attached storage (DAS) was accessed using SCSI protocols. When storage moved away from the processing unit, FC allowed the reach of SCSI's block-level access to storage media to be extended over much longer distances. Fibre Channel is most commonly used for attaching SANs, while NAS devices use either CIFS- or NFS-based file-level access over Ethernet links. Today, many network-attached storage devices – offering so-called multiprotocol or unified storage -- can also attach using FC and, more recently, iSCSI, which allows block-level access over IP via an Ethernet link, which means access to storage can be global.

NAS gateways

NAS devices are also deployed as front-end devices, gateways or heads for storage-area networks (SANs), where they act as file servers. In this role they manage block-level storage over Fibre Channel (FC) or iSCSI links.

Find more network attached storage (NAS) product information

Replication is the process of ensuring that a second copy of the data always exists. Array-based replication means there is a duplicate NAS that contains a mirror of the data. While most RAID configurations provide array-based replication, some also offer network replication, which means intercepting data being sent to and from the hosts, and copying it to another, usually remote, location.

Thin provisioning

Thin provisioning is a common feature in the latest NAS products. It allows storage managers to provision more storage to applications than is physically present, meaning you only buy capacity when it is actually needed, which improves utilisation. Compared to the traditional model of buying all provisioned storage upfront, this cuts capital and operational expenditures and you don't pay for the energy needed to spin and cool empty disks.

Tiered storage

Tiering involves moving infrequently accessed data onto cheaper storage. For example, high-speed but costly NAS devices might contain production data for live projects but, if a file hasn't been accessed for a given time -- maybe 90 days -- then it can be moved to a cheaper set of lower-performing disks. In a three-tier system, a file would be archived off to tape after a further period, maybe a year. An automated, policy-based system can perform these tasks, creating file pointers on higher tiers so that users can still access the files.

Virtual tape libraries

Virtual tape library functionality is included in some NAS products. VTLs are designed to look like tape drives and libraries from the point of view of the backup software, but consist of disks. They are often used in front of real tape libraries to speed access to infrequently accessed data and, because disks are faster than tape, to shorten backup windows.

Network attached storage vendor/product guide

Vendors that sell their own NAS technologies are relatively few: many resell or adapt the technology of others. Fujitsu sells a number of vendors' devices, Hitachi Data Systems resells BlueArc, IBM resells NetApp, and HP and Dell use Microsoft Windows Storage Server and Linux as the basis for their network attached storage products. Management software adds such NAS features as data deduplication, replication and thin provisioning.

Feature overlap across vendor offerings is very high, so most vendors offer features such as deduplication, tiering and thin provisioning, along with multiprotocol access, including iSCSI. The main differentiation inside vendor products remains capacity, performance and I/O capability, as well as added features such as data policy-based tools for data migration across tiered infrastructures and storage virtualisation.

Celerra GatewayNS-G2Max capacity: 128 TBMax ports: Four Fibre Channel, four 1 Gbps or two 10 Gbps and two 1Gbps per blade with maximum of two bladesKey features: Multiprotocol SAN gateway, file-level retention, data deduplication

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